bsc: Factor out duplicated code into f_exp_chan_rel_and_clear()

There's a sequence of commands which was repeated over at least
four test cases.  Let's factor this out into the new
f_exp_chan_rel_and_clear() function, and use that function from
all the former copy+pasted sections.

Change-Id: Ic6791fce4e8787e38b818a12ed526d3e47f313ef
1 file changed