sanity: Load arguments from files

Python module argparse has a feature to load arguments from a file.
This commit enables such feature on sanitycheck script so files
prefixed by + (plus sign) are loaded during argument parsing stage
and included as arguments to such script.

Jira: ZEP-122

Change-Id: Ibb0a6e8464218a4f58ce4044a5a0860dc5b32480
Signed-off-by: Genaro Saucedo Tejada <genaro.saucedo.tejada@intel.com>

scripts/sanity_chk/sanity_daily.args

@@ -0,0 +1,3 @@
+--inline-logs
+--all
+--enable-slow

scripts/sanity_chk/sanity_verify.args

@@ -0,0 +1,3 @@
+--inline-logs
+--exclude-tag
+footprint

scripts/sanitycheck

@@ -150,6 +150,10 @@ Metrics (such as pass/fail state and binary size) for the last code
 release are stored in scripts/sanity_chk/sanity_last_release.csv.
 To update this, pass the --all --release options.
 
+To load arguments from a file, write '+' before the file name, e.g.,
++file_name. File content must be one or more valid arguments separated by
+line break instead of white spaces.
+
 Most everyday users will run with no arguments.
 """
 
@@ -1607,6 +1611,7 @@ def parse_arguments():
 
     parser = argparse.ArgumentParser(description = __doc__,
                                      formatter_class = argparse.RawDescriptionHelpFormatter)
+    parser.fromfile_prefix_chars = "+"
 
     parser.add_argument("-p", "--platform", action="append",
             help="Platform filter for testing. This option may be used multiple "