Added braces around python variable to avoid Puppet syntax errors in install manifest
Specifically looked for the activate script when creating a virtualenv since this is created last.  This ensures that a half-created virtualenv will be detected and corrected by Puppet.
Added owner, group to the pip class which ensures that packages will be installed with the correct permissions.
Added environment attribute to the pip class which allows for users to override environment variables like LD_LIBRARY_PATH and ORACLE_HOME which are needed to install packages like cx_Oracle.