Tidy up the SSH call to avoid injection attacks for HP's driver

Let the command and arguments form up a list and avoid the extra arguments
attackers inserted to the command string.

And modify the interface of _cli_run, there is no need for a extra argument.

fix bug 1192971
Change-Id: Iff6a3ecb64feccae1b29164117576cab9943200a
Replace os.unlink with delete_if_exists

Shouldn't care when doing unlink on our temp files
if they exist or not.  In fact this causes problems
when you do things like with tempfile/dir and happen
to try and unlink after it's already been removed.

This replaces these calls with the safer
common.fileutils.delete_if_exists which will
ignore the os exception of the object DNE.

Fixes bug: 1212502

Change-Id: Ica86c95f736411da486335aec5512e59247bfbc0
Merge "Tidy up the SSH call to avoid injection attacks for HP's driver"
Merge "Replace os.unlink with delete_if_exists"