Fix a bug that may cause the ota generation fail.
Fix a bug that may cause the ota generation fail.

The extra space in args['extra'] may cause the ota generation fail.

Test: python test_ota_interface.py -v
Change-Id: Iac6d06a89c52ab7554e54c08e5e04496b3da730a

google/ota-generator,google/ota-generator,google/ota-generator,google/ota-generator