Make getvar return a dictionary from a single bootloader variable

So say you do:
>>> getvar('ro.build.fingerprint')

You'll get a dictionary of:
{'ro.build.fingerprint': 'motorola/ghost_att/ghost:4.2.2/13.9.0Q2.X-116-X-17-51/12:us'}

Signed-off-by: Bryan Hundven <bryanhundven@gmail.com>