+ """Parse arguments, perform the action, write useful output, propagate RC.
+
+ If the intended action is cancellation, reservation dir is deleted.
+
+ If the intended action is reservation, the list is longer:
+ 1. List contents of reservation dir.
+ 2. List contents of test.url file in the dir.
+ 3. Create reservation dir.
+ 4. Touch file according to -r option.
+ From these 4 steps, 1 and 2 are performed always, their RC ignored.
+ RC of step 3 gives the overall result.
+ If the result is success, step 4 is executed without any output,
+ their RC is ignored.
+
+ The "run tag" as a filename is useful for admins accessing the testbed
+ via a graphical terminal, which does not allow copying of text,
+ as they need less keypresses to identify the test run holding the testbed.
+ Also, the listing shows timestamps, which is useful for both audiences.
+
+ This all assumes the target system accepts ssh connections.
+ If it does not, the caller probably wants to stop trying
+ to reserve this system. Therefore this script can return 3 different codes.
+ Return code 0 means the reservation was successful.
+ Return code 1 means the system is inaccessible (or similarly unsuitable).
+ Return code 2 means the system is accessible, but already reserved.
+ The reason unsuitable systems return 1 is because that is also the value
+ Python returns on encountering and unexcepted exception.
+ """