Replace the "coldboot" timeout with a property.

Also rename init's existing boot-time related properties so they're
all "ro.*" properties.

Example result:

  # Three properties showing when init started...
  [ro.boottime.init]: [5294587604]
  # ...how long it waited for ueventd...
  [ro.boottime.init.cold_boot_wait]: [646956470]
  # ...and how long SELinux initialization took...
  [ro.boottime.init.selinux]: [45742921]

  # Plus one property for each service, showing when it first started.
  [ro.boottime.InputEventFind]: [10278767840]
  [ro.boottime.adbd]: [8359267180]
  [ro.boottime.atfwd]: [10338554773]
  [ro.boottime.audioserver]: [10298157478]
  [ro.boottime.bootanim]: [9323670089]
  [ro.boottime.cameraserver]: [10299402321]
  [ro.boottime.cnd]: [10335931856]
  [ro.boottime.debuggerd]: [7001352774]
  [ro.boottime.debuggerd64]: [7002261785]
  [ro.boottime.drm]: [10301082113]
  [ro.boottime.fingerprintd]: [10331443314]
  [ro.boottime.flash-nanohub-fw]: [6995265534]
  [ro.boottime.gatekeeperd]: [10340355242]
  [ro.boottime.healthd]: [7856893380]
  [ro.boottime.hwservicemanager]: [7856051088]
  [ro.boottime.imscmservice]: [10290530758]
  [ro.boottime.imsdatadaemon]: [10358136702]
  [ro.boottime.imsqmidaemon]: [10289084872]
  [ro.boottime.installd]: [10303296020]
  [ro.boottime.irsc_util]: [10279807632]
  [ro.boottime.keystore]: [10305034093]
  [ro.boottime.lmkd]: [7863506714]
  [ro.boottime.loc_launcher]: [10324525241]
  [ro.boottime.logd]: [6526221633]
  [ro.boottime.logd-reinit]: [7850662702]
  [ro.boottime.mcfg-sh]: [10337268315]
  [ro.boottime.media]: [10312152687]
  [ro.boottime.mediacodec]: [10306852530]
  [ro.boottime.mediadrm]: [10308707999]
  [ro.boottime.mediaextractor]: [10310681177]
  [ro.boottime.msm_irqbalance]: [7862451974]
  [ro.boottime.netd]: [10313523104]
  [ro.boottime.netmgrd]: [10285009351]
  [ro.boottime.oem_qmi_server]: [10293329092]
  [ro.boottime.per_mgr]: [7857915776]
  [ro.boottime.per_proxy]: [8335121605]
  [ro.boottime.perfd]: [10283443101]
  [ro.boottime.qcamerasvr]: [10329644772]
  [ro.boottime.qmuxd]: [10282346643]
  [ro.boottime.qseecomd]: [6855708593]
  [ro.boottime.qti]: [10286196851]
  [ro.boottime.ril-daemon]: [10314933677]
  [ro.boottime.rmt_storage]: [7859105047]
  [ro.boottime.servicemanager]: [7864555881]
  [ro.boottime.ss_ramdump]: [8337634938]
  [ro.boottime.ssr_setup]: [8336268324]
  [ro.boottime.surfaceflinger]: [7866921402]
  [ro.boottime.thermal-engine]: [10281249924]
  [ro.boottime.time_daemon]: [10322006542]
  [ro.boottime.ueventd]: [5618663938]
  [ro.boottime.vold]: [7003493920]
  [ro.boottime.wificond]: [10316641073]
  [ro.boottime.wpa_supplicant]: [18959816881]
  [ro.boottime.zygote]: [10295295029]
  [ro.boottime.zygote_secondary]: [10296637269]

Bug: http://b/31800756
Test: boots
Change-Id: I094cce0c1bab9406d950ca94212689dc2e15dba5