test: add TEST_SKIP to mkosi integration test wrapper

Takes a space-separate list of test names, allows to skip one or more tests

test/README.testsuite

@@ -237,6 +237,8 @@ or Debian's default kernel path and initrd are used by default.)
 A script will try to find your qemu binary. If you want to specify a different
 one with `$QEMU_BIN`.
 
+`TEST_SKIP`: takes a space separated list of tests to skip.
+
 ### Debugging the qemu image
 
 If you want to log in the testsuite virtual machine, use `TEST_SHELL=1`

test/integration-test-wrapper.py

@@ -61,6 +61,10 @@ def main():
         print(f"TEST_NO_QEMU=1, skipping {args.name}", file=sys.stderr)
         exit(77)
 
+    if args.name in os.getenv("TEST_SKIP", "").split():
+        print(f"Skipping {args.name} due to TEST_SKIP", file=sys.stderr)
+        exit(77)
+
     keep_journal = os.getenv("TEST_SAVE_JOURNAL", "fail")
     shell = bool(int(os.getenv("TEST_SHELL", "0")))