Issue:
------
File operations in MTR tests fail sometimes due to environmental
issues on certain platforms. To overcome this problem, a retry
argument was requested for the file operations.

Fix:
----
Six file operations in MTR now have an optional retry argument,
which when specified, retries the operation a given number of
times at an interval of one second each. remove_file, move_file,
file_exists, remove_files_wildcard, copy_files_wildcard, and
copy_file have this optional argument.

The usage is as follows:
--<file_operation> <file_names(s)> [<retry>]

This fix also made the pattern argument in remove_files_wildcard
and copy_files_wildcard mandatory.

Reviewed-by: Pavan Naik <pavan.naik@oracle.com>
Reviewed-by: Srikanth B R <srikanth.b.r@oracle.com>
Reviewed-by: Yashwant Sahu <yashwant.sahu@oracle.com>
RB: 16667