Add option to call signing server via sign_formal_patch.sh
script (same process used by CentOS).
Test Plan:
Pass: build a patch with --formal
Pass: Upload and apply patch with Formal key
Story: 2009969
Task: 45573
Signed-off-by: Luis Sampaio <luis.sampaio@windriver.com>
Change-Id: Iba7c6ddc62aa40c323d7f56514b7a27c198168a5