R4.0 rc3 qvm-check's output and retcode kind of buggy

[taradiddles]

Qubes OS version:

R4.0 rc3

---

Steps to reproduce the behavior:

I'm scripting some stuff in dom0 and need to check if a VM exists ; qvm-check seems to be the way to go rather than grepping the output of qvm-ls.

Let's assume that a VM named "work" exists and that a VM named "work1" doesn't.

Case 1: checking if VM "work" is running: works as expected

[user@dom0 ~]$ qvm-check work
VM work exists
[user@dom0 ~]$ echo $?
0

Case 2: adding the --quiet arg: the output isn't suppressed

[user@dom0 ~]$ qvm-check --quiet work
VM work exists

Case 3: finding out what the retcode for a wrong syntax is (to compare with case 4 below)

[user@dom0 ~]$ qvm-check --blahblah
[...]
[user@dom0 ~]$ echo $?
2

Case 4: checking if a non existent VM exists: usage() is displayed and usage()'s retcode is returned despite the syntax being right; one would expect the retcode "1"

[user@dom0 ~]$ qvm-check work1
usage: qvm-check [-h] [--verbose] [--quiet] [--all] [--exclude EXCLUDE]
                 [--running] [--paused] [--template]
                 [VMNAME [VMNAME ...]]
qvm-check: error: no such domain: 'work1'
[user@dom0 ~]$ echo $?
2

I looked at /usr/lib/python3.5/site-packages/qubesadmin/tests/tools/qvm_check.py to try to fix it and send a PR, but it was a bit too cryptic for me.

Very minor issue BTW.