Fix EE volume mount issue

[cidrblock]

When working on #1059 I noticed this:

The issue was a EEV entry with source of C.PREVIOUS_CLI was being processed as if it was a settings file entry, it can be seen:

220307235030.086 WARNING 'ansible_navigator.actions.config._update_args' The following execution-environment.volume-mounts entry could not be parsed: /home/collections:/tmp/collections_to_volmount:z
220307235030.086 INFO 'ansible_navigator.actions.config._update_args' The value of execution-environment.volume-mounts should be list of dictionaries and valid keys are 'src', 'dest' and 'label'.

Overview:

• Add a from_string and from_dictionary method to VolumeMount
• Refactor execution_environment_volume_mounts to build a list of VolumeMount
• Check the source of all volume mounts and exit early if one is not real
• Update tests to use /tmp instead of fake directories to avoid the early exit
• Added per SettingsEntry env var split character to account for a , in the EE volmounts

Some more tests coming as well.