Server 3.0: emmc-wait: Increase timeout to 15 minutes

During installs, the security service needed to unlock the eMMC takes
more than 5 minutes to become available. So increase the timeout to
15 minutes.

Tested: Built
Fusion-Link: fusion2/NA
Platforms-Affected: Server 3.0 platforms.
Google-Bug-Id: 542303598
Change-Id: I272bfd1eaee775fe3eb371ef676f95c40f2b0ed7
Signed-off-by: Vivekanand Veeracholan <vveerach@google.com>
(cherry picked from commit adef9d0f3acae77ab6706b52e1afd8f26a69b26e)

recipes-google/gbmc-sysinit/server3/wait_emmc_available.sh

diff --git a/recipes-google/gbmc-sysinit/server3/wait_emmc_available.sh b/recipes-google/gbmc-sysinit/server3/wait_emmc_available.sh
index 069fd1c..6bf7ba3 100644
--- a/recipes-google/gbmc-sysinit/server3/wait_emmc_available.sh
+++ b/recipes-google/gbmc-sysinit/server3/wait_emmc_available.sh
@@ -4,7 +4,7 @@
 # timing out after a specified duration.
 
 main() {
-  local -r timeout_seconds=300
+  local -r timeout_seconds=900
   local -r sleep_interval_seconds=30
   local start_time
   start_time=$SECONDS