utilities: Fix and unify parsing of timeout option.

utilities: Fix and unify parsing of timeout option.

Parsing of the '--timeout' option implemented differently
for every single control utility and, which is more
important, highly inaccurate. In most cases unsigned result
of 'strtoul' stored in signed variable. Parsing failures are
not tracked. 'ovs-appctl' even uses just 'atoi' without any
checking of the argument or result.

This patch unifies the parsing by using 'str_to_uint'.

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>