(PUP-10015) Add support for arbitrary equality to pip provider

[joshcooper]

Without this patch the pip provider doesn't correctly parse pip freeze
output specified with arbitrary equality.

https://www.python.org/dev/peps/pep-0440/#arbitrary-equality

This is manifest with triple === separating the package name from the
package version, e.g.

$ pip freeze | grep pytz
pytz===2012f

By not correctly parsing this output, puppet tries to continually
install this package on each run.

The patch updates the regex to handle arbitrary equality.

[joshcooper]

This was already approved in the PR targeting master.

[maltewhiite]

@joshcooper
I am having this issue.

$python_packages = ['argparse', 'regex', 'prometheus_client']
  package { $python_packages:
    ensure   => installed,
    provider => pip3,
}

causes this every time:

Notice: /Stage[main]/Monitoring/Package[argparse]/ensure: created
Notice: /Stage[main]/Monitoring/Package[prometheus_client]/ensure: created

Workaround

  package { 'regex':
    ensure   => installed,
    provider => pip3,
  }

  package { ['python-argparse', 'python2-prometheus_client']:
    ensure   => installed,
    provider => yum,
  }