Pip's name key can now accept remote package address.

Summary:

Current implementation of Pip module does not allow remote package address if the user only wants to specify using name='url' instead of a requirement file.

Furthermore, the module requires either name or requirement as a
required key, although the documentation table said neither is required.
The fact that one of them must be present is not documented in the
documentation causes confusion. This commit added this fact as part of
description.

If the user uses the remote serivice address as the name and the user does not supply -e option in extra_vars (which is the whole point of this commit), we will add -e to extra_vars so pip command can run with -e option.