Support more specific descriptors of a machine's OS in Machine Provider dimensions

appengine/components/components/machine_provider/dimensions.py

Index: appengine/components/components/machine_provider/dimensions.py
diff --git a/appengine/components/components/machine_provider/dimensions.py b/appengine/components/components/machine_provider/dimensions.py
index ed1fd194da5a1fe9d414d678c04b9e15aa001b67..9eb0a5814876b5ef3dd08ec6291c1ddd4c18d3df 100644
--- a/appengine/components/components/machine_provider/dimensions.py
+++ b/appengine/components/components/machine_provider/dimensions.py
@@ -21,6 +21,11 @@ class OSFamily(messages.Enum):
   WINDOWS = 3
 
 
+class LinuxFlavor(messages.Enum):
+  """Lists valid flavors of Linux."""
+  UBUNTU = 1
+
+
 class Dimensions(messages.Message):
   """Represents the dimensions of a machine."""
   # The operating system family of this machine.
@@ -37,3 +42,7 @@ class Dimensions(messages.Message):
   memory_gb = messages.FloatField(5)
   # The disk space available to this machine.
   disk_gb = messages.IntegerField(6)
+  # The flavor of Linux of this machine.
+  linux_flavor = messages.EnumField(LinuxFlavor, 7)

[Vadim Sh., 2016/11/10 23:37:08]

is there an advantage of having this separate instead of putting it into
os_version?

E.g. make os_version be "ubuntu-14.04"

[smut, 2016/11/11 00:14:14]

I have no strong feelings one way or the other.

I just did it this way because Swarming reports increasing specificity for Linux
this way, e.g. os: Linux | Ubuntu | Ubuntu-14.04 and because the user has less
to screw up in luci-config (e.g. capitalization: "Ubuntu-14.04" vs.
"ubuntu-14.04").

+  # The operating system version of this machine.
+  os_version = messages.StringField(8)