Fix activation of `_galaxy_` conda env

- Use `conda_activate`, which works also under dash
- Run `conda_activate` also when `$GALAXY_CONDA_ENV` already exists
- Run `virtualenv` when the conda env is active but `$GALAXY_VIRTUAL_ENV`
  does not exist
- Update the default for `GALAXY_CONDA_ENV` in
  scripts/common_startup_functions.sh

Follow-up on https://github.com/galaxyproject/galaxy/pull/6975 .

scripts/common_startup.sh

@@ -106,8 +106,7 @@ fi
 # GALAXY_CONDA_ENV is not set here because we don't want to execute the Galaxy version check if we don't need to
 
 if [ $SET_VENV -eq 1 -a $CREATE_VENV -eq 1 ]; then
-    if [ ! -d "$GALAXY_VIRTUAL_ENV" ]
-    then
+    if [ ! -d "$GALAXY_VIRTUAL_ENV" ]; then
         # Locate `conda` and set $CONDA_EXE (if needed). If `python` is Conda Python and $GALAXY_VIRTUAL_ENV does not
         # exist, virtualenv will not be used. setup_python calls this as well but in this case we need it done
         # beforehand.
@@ -121,12 +120,12 @@ if [ $SET_VENV -eq 1 -a $CREATE_VENV -eq 1 ]; then
                     echo "Creating Conda environment for Galaxy: $GALAXY_CONDA_ENV"
                     echo "To avoid this, use the --no-create-venv flag or set \$GALAXY_CONDA_ENV to an"
                     echo "existing environment before starting Galaxy."
-                    $CONDA_EXE create --yes --name "$GALAXY_CONDA_ENV" 'python=2.7' 'pip>=9' 'virtualenv>=16' -c 'conda-forge'
-                    source activate "$GALAXY_CONDA_ENV"
-                    virtualenv "$GALAXY_VIRTUAL_ENV"
+                    $CONDA_EXE create --yes --override-channels --channel conda-forge --channel defaults --name "$GALAXY_CONDA_ENV" 'python=2.7' 'pip>=9' 'virtualenv>=16'
                     unset __CONDA_INFO
                 fi
+                conda_activate
             fi
+            virtualenv "$GALAXY_VIRTUAL_ENV"
         else
             # If .venv does not exist, and there is no conda available, attempt to create it.
             # Ensure Python is a supported version before creating .venv

scripts/common_startup_functions.sh

@@ -77,7 +77,7 @@ run_common_start_up() {
 }
 
 conda_activate() {
-    : ${GALAXY_CONDA_ENV:="_galaxy_$(get_galaxy_major_version)"}
+    : ${GALAXY_CONDA_ENV:="_galaxy_"}
     echo "Activating Conda environment: $GALAXY_CONDA_ENV"
     # Dash is actually supported by 4.4, but not with `. /path/to/activate`, only `conda activate`, which we
     # can't load unless we know the path to <conda_root>/etc/profile.d/conda.sh
@@ -106,7 +106,7 @@ setup_python() {
     elif [ -z "$skip_venv" ]; then
         set_conda_exe
         if [ -n "$CONDA_EXE" ] && \
-                check_conda_env ${GALAXY_CONDA_ENV:="_galaxy_$(get_galaxy_major_version)"}; then
+                check_conda_env ${GALAXY_CONDA_ENV:="_galaxy_"}; then
             # You almost surely have pip >= 8.1 and running `conda install ... pip>=8.1` every time is slow
             REPLACE_PIP=0
             [ -n "$PYTHONPATH" ] && { echo 'Unsetting $PYTHONPATH'; unset PYTHONPATH; }
@@ -181,10 +181,6 @@ find_server() {
     fi
 }
 
-get_galaxy_major_version() {
-    PYTHONPATH='lib' python -c 'from galaxy.version import VERSION_MAJOR; print(VERSION_MAJOR)'
-}
-
 # Prior to Conda 4.4, the setup method was to add <conda_root>/bin to $PATH. Beginning with 4.4, that method is still
 # possible, but the preferred method is to source <conda_root>/etc/profile.d/conda.sh. If the new method is used, the
 # base environment will *not* be on $PATH, unlike previous versions, and `conda` is a shell function not available to
@@ -235,11 +231,11 @@ check_conda_env() {
     # envs listed in ~/.conda/environments.txt show up in envs.txt but can't be activated by name. =/
     set_conda_info
     printf "%s" "$__CONDA_INFO" \
-        | python -c "import json, os.path, sys; info=json.load(sys.stdin); sys.exit(0 if '$1' in [os.path.basename(p) for p in info['envs'] if os.path.dirname(p) in info['envs_dirs']] else 1)"
+        | python -c "import json, os.path, sys; info = json.load(sys.stdin); sys.exit(0 if '$1' in [os.path.basename(p) for p in info['envs'] if os.path.dirname(p) in info['envs_dirs']] else 1)"
 }
 
 get_conda_env_path() {
     set_conda_info
     printf "%s" "$__CONDA_INFO" \
-        | python -c "import json, os.path, sys; info=json.load(sys.stdin); print([p for p in info['envs'] if os.path.basename(p) == '$1' and os.path.dirname(p) in info['envs_dirs']][0])"
+        | python -c "import json, os.path, sys; info = json.load(sys.stdin); print([p for p in info['envs'] if os.path.basename(p) == '$1' and os.path.dirname(p) in info['envs_dirs']][0])"
 }