Fixes #311

There currently exists a discrepency between the param types expected
from:
1. The parts library and in generate / prototype use
2. ks param set

ks param set will set boolean types as jsonnet boolean types, however,
prototypes will set boolean types as strings (i.e. in quotes). This
change will make it such that ks param sets boolean types as strings.
The reason we're not setting booleans in both model is because that will
require a better dependency story around ksonnet/parts first.

Signed-off-by: Jessica Yuen <im.jessicayuen@gmail.com>