#8265: config: make int parser accept K, M, G, T, P suffix and scale value accordingly

We are allowing this for all and any integer values; that is, OPT_INT,
OPT_LONGLONG, OPT_U32 and OPT_U64.

It's on the user to use appropriate units.  For instance, the user should
not use 'E(xabyte)' when setting a signed int, and use his best judgment
when setting options that, for instance, ought to receive seconds.

Fixes: 8265
Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>

Patch series also adds function 'strict_strtosi()', which takes a string
and returns an appropriately scaled uint64_t value, and unit tests both
for the function (test/strtol.cc) and for the argument parsing via the ceph
tool.