scripts/yocto_testresults_query: add option to change display limit

scripts/yocto_testresults_query: add option to change display limit

Add a "-l"/"--limit" option to allow changing the display limit in
resulttool.
- If no value is passed, resulttool uses its default value.
- If 0 is passed, the display limit is removed and every regression will be
  displayed
- If a custom value is passed, this value overrides the vlaue configured in
  resulttool

Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>