Use __utils__ instead of salt.utils.cloud in opennebula driver

[rallytime]

What does this PR do?

In #35483, we switched to using __utils__['cloud.some_function'] instead of salt.utils.cloud.some_function. Some of the references were missed in the opennebula cloud driver. This PR fixes those references.

It also fixes up the from salt.utils import is_true references. Whenever we are using functions from salt.utils.__init__.py we need to import the whole module and reference functions explicitly. This PR changes the is_true references to salt.utils.is_true to match the salt.utils.fopen calls.

What issues does this PR fix or reference?

Fixes #36057

Previous Behavior

[ERROR   ] There was a profile error: global name '__opts__' is not defined
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/salt/cloud/cli.py", line 284, in run
    self.config.get('names')
  File "/usr/lib/python2.7/dist-packages/salt/cloud/__init__.py", line 1451, in run_profile
    ret[name] = self.create(vm_)
  File "/usr/lib/python2.7/dist-packages/salt/cloud/__init__.py", line 1281, in create
    output = self.clouds[func](vm_)
  File "/usr/lib/python2.7/dist-packages/salt/cloud/clouds/opennebula.py", line 956, in create
    ret = salt.utils.cloud.bootstrap(vm_, __opts__)
  File "/usr/lib/python2.7/dist-packages/salt/utils/cloud.py", line 514, in bootstrap
    transport=opts.get('transport', 'zeromq')
  File "/usr/lib/python2.7/dist-packages/salt/utils/cloud.py", line 1721, in fire_event
    sock_dir = os.path.join(__opts__['sock_dir'], 'master')
NameError: global name '__opts__' is not defined

New Behavior

Cleans up the stack trace and fixes the problem.

Tests written?

No

Please review Salt's Contributing Guide for best practices.

[rallytime]

I need to backport this to 2015.8, too.

[cachedout]

@rallytime and @gtmanfred Could you please investigate the test failures here?

[rallytime]

The failing tests should be fixed now.

[cachedout]

Thank you, @rallytime