tools: Allow optional arguments after file arguments in test_backend.
tools: Allow optional arguments after file arguments in test_backend.

Fixes #9233.
Uses nargs='*' instead of nargs='argparse.REMAINDER'.
nargs='argparse.REMAINDER' gathers remaining terms as arguments
even if it is an option e.g --coverage, while '*' gathers all the
command-line arguments until the next option is encountered.

showell/zulip,rht/zulip,eeshangarg/zulip,zulip/zulip,shubhamdhama/zulip,hackerkid/zulip,shubhamdhama/zulip,showell/zulip,timabbott/zulip,tommyip/zulip,kou/zulip,dhcrzf/zulip,kou/zulip,punchagan/zulip,tommyip/zulip,dhcrzf/zulip,synicalsyntax/zulip,rishig/zulip,zulip/zulip,eeshangarg/zulip,hackerkid/zulip,kou/zulip,eeshangarg/zulip,showell/zulip,dhcrzf/zulip,synicalsyntax/zulip,rht/zulip,kou/zulip,timabbott/zulip,andersk/zulip,brainwane/zulip,synicalsyntax/zulip,timabbott/zulip,jackrzhang/zulip,zulip/zulip,andersk/zulip,rht/zulip,dhcrzf/zulip,synicalsyntax/zulip,rishig/zulip,shubhamdhama/zulip,rht/zulip,jackrzhang/zulip,punchagan/zulip,tommyip/zulip,tommyip/zulip,punchagan/zulip,jackrzhang/zulip,brainwane/zulip,timabbott/zulip,brainwane/zulip,jackrzhang/zulip,tommyip/zulip,punchagan/zulip,showell/zulip,brainwane/zulip,rishig/zulip,brainwane/zulip,hackerkid/zulip,tommyip/zulip,dhcrzf/zulip,zulip/zulip,hackerkid/zulip,jackrzhang/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,showell/zulip,punchagan/zulip,brainwane/zulip,tommyip/zulip,andersk/zulip,shubhamdhama/zulip,hackerkid/zulip,showell/zulip,dhcrzf/zulip,synicalsyntax/zulip,shubhamdhama/zulip,andersk/zulip,shubhamdhama/zulip,shubhamdhama/zulip,eeshangarg/zulip,punchagan/zulip,dhcrzf/zulip,timabbott/zulip,rht/zulip,timabbott/zulip,punchagan/zulip,eeshangarg/zulip,andersk/zulip,kou/zulip,rishig/zulip,zulip/zulip,andersk/zulip,hackerkid/zulip,eeshangarg/zulip,rishig/zulip,zulip/zulip,synicalsyntax/zulip,showell/zulip,timabbott/zulip,jackrzhang/zulip,rishig/zulip,hackerkid/zulip,synicalsyntax/zulip,jackrzhang/zulip,brainwane/zulip,rht/zulip,rishig/zulip,kou/zulip,rht/zulip,andersk/zulip