Revert of Use -s to pass string date to 'adb shell date' command to set date...

Revert of Use -s to pass string date to 'adb shell date' command to set date in provision. (patchset #1 id:1 of https://codereview.chromium.org/668013003/)

Reason for revert:
Broke the same tests mentioned on the bug on existing android bots, ex:
https://build.chromium.org/p/chromium.linux/builders/Android%20Tests%20%28dbg%29/builds/23612
https://build.chromium.org/p/chromium.linux/builders/Android%20Tests/builds/16366

Original issue's description:
> Use -s to pass string date to 'adb shell date' command to set date in provision.
>
> The 'date -u' was not working on N5 devices. The -s option seems to work across
> devices. I've tested on N4 and N5.
>
> BUG=406848
>
> Committed: https://crrev.com/e3b2f5071ae50778f07abbc84fc6a9e07e169892
> Cr-Commit-Position: refs/heads/master@{#300542}

TBR=zty@chromium.org,jbudorick@chromium.org,yfriedman@google.com,navabi@google.com
NOTREECHECKS=true
NOTRY=true
BUG=406848

Review URL: https://codereview.chromium.org/667303002

Cr-Commit-Position: refs/heads/master@{#300557}

build/android/provision_devices.py

@@ -190,8 +190,7 @@ def ProvisionDevice(device, options, is_perf):
                      battery_info.get('level', 0))
         time.sleep(60)
         battery_info = device.old_interface.GetBatteryInfo()
-    device.RunShellCommand('date -s %s' % time.strftime('%Y%m%d.%l%M%S'),
-                           as_root=True)
+    device.RunShellCommand('date -u %f' % time.time(), as_root=True)
     # TODO(jbudorick): Tune the timeout per OS version.
     device.Reboot(True, timeout=600, retries=0)
     props = device.RunShellCommand('getprop')