common/strtol.cc: strict_strtosi() converts str with SI units to uint64_t

Accepts values with a suffix (B, K, M, G, T, P, E) and returns the
appropriate byte value.

E.g., 10B = 10, while 10K = 10240.

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
test/strtol.cc: Test 'strict_strtosi()'

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
common/config.cc: allow integer values to be parsed as SI units

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>
qa/workunits/cephtool: test setting options using SI units

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>