Add API to install resolver tool dependencies

and to build a tool dependency cache (if activated in galaxy.ini).

An example to install dependencies for the twobit converter:
```
import bioblend.galaxy
url = 'http://localhost:8080/'
api_key = 'admin_api_key'
tool_id = 'CONVERTER_fasta_to_2bit'
endpoint = "api/tools/%s/install_dependencies" % tool_id
gi = bioblend.galaxy.GalaxyInstance(url, api_key)
gi.make_post_request("/".join((url, endpoint)), payload={'id': tool_id})
```
If `use_cached_dependency_manager` is activated in the galaxy.ini,
a cached environment can be built like this:
```
endpoint = "api/tools/%s/build_dependency_cache" % tool_id
gi.make_post_request("/".join((url, endpoint)), payload={'id': tool_id})
```

lib/galaxy/datatypes/converters/fasta_to_2bit.xml

@@ -2,6 +2,7 @@
     <!-- <description>__NOT_USED_CURRENTLY_FOR_CONVERTERS__</description> -->
     <!-- Used on the metadata edit page. -->
     <requirements>
+        <requirement type="package" version="332">ucsc-twobittofa</requirement>
         <requirement type="package">ucsc_tools</requirement>
     </requirements>
     <command>faToTwoBit '$input' '$output'</command>

lib/galaxy/webapps/galaxy/api/tools.py

@@ -129,6 +129,33 @@ class ToolsController( BaseAPIController, UsesVisualizationMixin ):
         tool = self._get_tool(id)
         return tool.tool_requirements_status
 
+    @expose_api
+    @web.require_admin
+    def install_dependencies(self, trans, id, **kwds):
+        """
+        POST /api/tools/{tool_id}/install_dependencies
+        Attempts to install requirements via the dependency resolver
+        """
+        tool = self._get_tool(id)
+        [tool._view.install_dependency(id=None, **req.to_dict()) for req in tool.requirements]
+        if kwds.get('build_dependency_cache'):
+            tool.build_dependency_cache()
+        # TODO: rework resolver install system to log and report what has been done.
+        # _view.install_dependency should return a dict with stdout, stderr and success status
+        return tool.tool_requirements_status
+
+    @expose_api
+    @web.require_admin
+    def build_dependency_cache(self, trans, id, **kwds):
+        """
+        POST /api/tools/{tool_id}/build_dependency_cache
+        Attempts to cache installed dependencies.
+        """
+        tool = self._get_tool(id)
+        tool.build_dependency_cache()
+        # TODO: Should also have a more meaningful return.
+        return tool.tool_requirements_status
+
     @expose_api
     @web.require_admin
     def diagnostics( self, trans, id, **kwd ):

lib/galaxy/webapps/galaxy/buildapp.py

@@ -262,6 +262,8 @@ def populate_api_routes( webapp, app ):
     webapp.mapper.connect( '/api/tools/{id:.+?}/citations', action='citations', controller="tools" )
     webapp.mapper.connect( '/api/tools/{id:.+?}/download', action='download', controller="tools" )
     webapp.mapper.connect( '/api/tools/{id:.+?}/requirements', action='requirements', controller="tools")
+    webapp.mapper.connect( '/api/tools/{id:.+?}/install_dependencies', action='install_dependencies', controller="tools", conditions=dict( method=[ "POST" ] ))
+    webapp.mapper.connect( '/api/tools/{id:.+?}/build_dependency_cache', action='build_dependency_cache', controller="tools", conditions=dict( method=[ "POST" ] ))
     webapp.mapper.connect( '/api/tools/{id:.+?}', action='show', controller="tools" )
     webapp.mapper.resource( 'tool', 'tools', path_prefix='/api' )