git-p4: pass command arguments as lists instead of using shell

git-p4: pass command arguments as lists instead of using shell

In the majority of the subprocess calls where shell=True was used, it
was only needed to parse command arguments by spaces. In each of these
cases, the commands are now being passed in as lists instead of strings.

This change aids the comprehensibility of the code. Constucting commands
and arguments using strings risks bugs from unsanitized inputs, and the
attendant complexity of properly quoting and escaping command arguments.

Signed-off-by: Joel Holdsworth <jholdsworth@nvidia.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>