Fix Ansible 2.9 incompatibility

[RobinDaugherty]

This might affect previous 2.x releases as well. Two things changed:

1. ansible-vault will no longer accept the --vault-password-file argument before the command.
2. The output of ansible-vault --help no longer contains "Usage" followed by the list of commands. It looks like this:

usage: ansible-vault [-h] [--version] [-v]
                     {create,decrypt,edit,view,encrypt,encrypt_string,rekey}
                     ...

encryption/decryption utility for Ansible data files

positional arguments:
  {create,decrypt,edit,view,encrypt,encrypt_string,rekey}
    create              Create new vault encrypted file
    decrypt             Decrypt vault encrypted file
    edit                Edit vault encrypted file
    view                View vault encrypted file
    encrypt             Encrypt YAML file
    encrypt_string      Encrypt a string
    rekey               Re-key a vault encrypted file

optional arguments:
  --version             show program's version number, config file location,
                        configured module search path, module location,
                        executable location and exit
  -h, --help            show this help message and exit
  -v, --verbose         verbose mode (-vvv for more, -vvvv to enable
                        connection debugging)

See 'ansible-vault <command> --help' for more information on a specific
command.

I updated the usage of ansible-vault to place the view command before the other arguments.

I changed the dependency check to look for "view" in the help output, with word boundaries.

I believe both of these changes will support older versions of Ansible, but I did not test on every possible version to be sure.