Add a function to get the current time in microseconds
Add a function to get the current time in microseconds

In some cases we need higher resolution that seconds; I've settled on
microseconds as that is what 'threadDelay' wants, for exactly, so it's
easier if we keep the same units.

Signed-off-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>
Reviewed-by: Michele Tartara <05f7077a2c6cbbdc4af4ba42e3ef89a0df846179@google.com>

grnet/snf-ganeti,yiannist/ganeti,bitemyapp/ganeti,apyrgio/snf-ganeti,leshchevds/ganeti,dimara/ganeti,mbakke/ganeti,ganeti/ganeti,apyrgio/ganeti,onponomarev/ganeti,apyrgio/ganeti,onponomarev/ganeti,ganeti-github-testing/ganeti-test-1,dimara/ganeti,andir/ganeti,yiannist/ganeti,yiannist/ganeti,mbakke/ganeti,andir/ganeti,apyrgio/snf-ganeti,ganeti/ganeti,andir/ganeti,mbakke/ganeti,bitemyapp/ganeti,leshchevds/ganeti,ganeti-github-testing/ganeti-test-1,grnet/snf-ganeti,leshchevds/ganeti,ganeti/ganeti