cp.get_file_str: do not fail if file not found

[vutny]

What does this PR do?

It removes misleading exception message when cp.get_file_str function tries to display non-existent file:

Passed invalid arguments: coercing to Unicode: need string or buffer, bool found.

Instead, the function will simply return the result given by cache_file function which does the real job.

This becomes especially useful in Jinja templates.

Previous Behavior

# salt-call cp.get_file_str salt://files/test2
[ERROR   ] Unable to cache file u'salt://files/test2' from saltenv 'base'.

Passed invalid arguments: coercing to Unicode: need string or buffer, bool found.

Usage:

    Return the contents of a file from a URL

    CLI Example:

    .. code-block:: bash

        salt '*' cp.get_file_str salt://my/file

New Behavior

# salt-call cp.get_file_str salt://files/test2
[ERROR   ] Unable to cache file u'salt://files/test2' from saltenv 'base'.
local:
    False

Tests written?

No

[rallytime]

This needs to be using six.string_type instead of str here.

Any reason you're not using os.path.exists or something similar instead of checking for a str type?

[vutny]

@rallytime Fixed, thanks!

os.path.exists(fn_) doesn't suit here, because it will throw TypeError if cache_file() function would return False (file cannot be cached for some reason). Too much logic to wrap around this simple check.

[rallytime]

Ah, right. That makes sense. Thanks!