common: replace uses of calloc(..., 1) with zmalloc

I found these uses of calloc, which could be replaced with zmalloc.  I
presumed that the reason for using calloc was for the fact that it
initializes the memory to zeroes.

Change-Id: Icd8b84d707978e949c55d9694e6dbc10319c0169
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>