Add a step for checking file existence (and properties)

[glum23]

Add a step into file_steps.py that will enable to check whether a file exists (and possibly has some properties like permissions, size, etc.).

[ignatenkobrain]

not sure, but probably easier would be to use test inline, but obviously would like to see some use-cases to find best solution

[glum23]

Well, it's always possible to call bash commands directly, however, it imho breaks the purpose of the behavioral framework. I needed it when checking results of dnf download.

[ignatenkobrain]

yeah, when talking about dnf-download it is perfectly valid use-case. Mind sending PR for checking that file exists?

[kkaarreell]

I propose to implement step like

Then the file {filepath} exists
 | tag    | value      |
 | size   | 12345      |
 | md5sum | 0123456abc |
 | perm   | 755        |

where the table part would be optional and we could add support for various file characteristics