replay: don't use rtc clock on loadvm phase

This patch disables the update of the periodic timer of mc146818rtc
in record/replay mode. State of this timer is saved and therefore does
not need to be updated in record/replay mode.
Read of RTC breaks the replay because all rtc reads have to be the same
as in record mode.

Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Message-Id: <20170124071730.4572.41874.stgit@PASHA-ISP>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
