Added an optional parameter to the 'list' method of
'EnvironmentManager' class to support the filtering of environment
list by the owner tenant (project)
Change-Id: I9195a30c287d56dedd12099843f2c131882079a5
Implements-blueprint: list-environments-of-a-given-project
Depends-on: I90b0dd672d5a431f63e52753d7f517fd3d0ec6eb