Reform energy output tests

Reform energy output tests

Separated tests of t_mdebin from tests of t_ebin to prepare for making
t_mdebin a proper class. Improved coverage of t_mdebin (and indirectly
t_ebin). Made done_ebin deallocate ebin, which means scoped_cptr is
now more usable.

Made some operations on t_mdebin more safe, by checking for nullptr or
reordering logic. Technically there are now two more branches when
writing energy output.

Change-Id: I4b056f660d16ce7af225e229030d6729a34acefe