Fix issues reported by ShellCheck in tsp

Fix issues reported by ShellCheck in tsp

Move check_diff() to tsp/jobs/img_test_common.sh
Add newline at the end of 'modifed_paths' in tsp/scripts/crawler.py
so that whole lines instead of words can be read.

ShellCheck: https://github.com/koalaman/shellcheck
shellcheck -e SC1090,SC2155,SC2068,SC2145,SC2164 `find tsp -name "*.sh"`

output should report following problems only:
    tsp/common.sh: SC2148, SC2034, SC2139
    tsp/jobs/trigger_downloads.sh: SC2115
    tsp/jobs/common_prep_flash_conf.sh: SC2029
    tsp/jobs/publish.sh: SC2046, SC2029

Change-Id: I7791769a0d653c784715cdd1a8b1446fafcba1e9
Signed-off-by: Aleksander Mistewicz <a.mistewicz@samsung.com>