testbench: accept ":*" as test iteration parameter for "runonly"

Without such a parameter it runs the first iteration. This is a change from
the previous form where the number's absence would refer to iter=0 regardless
of whether the test is even valid with that.

This suggests that the runonly syntax could accept references to testcases and
entire suites instead of shorthand for an entire test. That'd be more useful
for the test reporting script as well.
space: modify the page table in space_get_utcb_page()

When a new UTCB page must be allocated, it should be mapped into the address
space immediately.

However, it's also the case that when that page isn't mapped, the pagefault
handler should perform the exactly equivalent operation through mapdb. This
causes certain tests to fail, and the indirect ThreadControl operation in
forkserv's end_thread() to scream about failures and such. That symptom, as
well as the "many faults" report from forkserv in the UTCB range, suggests a
fuckup with regard to either the entire UTCB page, just the "UTCB area
pointer", or even the %gs register.