Enable ios on Raspberry Pi

Adds more jobs to iOS testing and switches to 
RPi based hosts. 

Bug: skia:
Change-Id: I0124c6554173fa3b22b077a198612bb30691d1fb
Reviewed-on: https://skia-review.googlesource.com/11521
Commit-Queue: Stephan Altmueller <stephana@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
diff --git a/infra/bots/recipes/perf.py b/infra/bots/recipes/perf.py
index 57ce232..2d3cef0 100644
--- a/infra/bots/recipes/perf.py
+++ b/infra/bots/recipes/perf.py
@@ -300,6 +300,7 @@
   env = {}
   if 'iOS' in api.vars.builder_name:
     env['IOS_BUNDLE_ID'] = 'com.google.nanobench'
+    env['IOS_MOUNT_POINT'] = api.vars.slave_dir.join('mnt_iosdevice')
   with api.env(env):
     try:
       if 'Chromecast' in api.vars.builder_name: