ota_from_target_files: remove duplicate setting of recovery_img

This variable is already set earlier in the script and does not need
to be wrapped inside of the if statement

Change-Id: I91b7f7d2fc911a3910b3df09cff0ca0f44fe7741
releasetools: Fix error text in ota_from_target_files

property isn't the variable name, prop is

Change-Id: I0fc6adddfd51ba9bc79f6559c61cd831203c9e3d
img_from_target_files: Create md5 hashes for each file

Generate an md5sum-fastboot.md5 file that contains an md5 hash of each
file in the fastboot zip and store the file in the zip.

Change-Id: I19c2ac5a84fb21e965953d1dad0ebcbfd0b78d47
releasetools: Properly handle custom values for tools

Rather than writing these values to their own files, store them
in the target_files META/misc_info.txt. This way, we don't need to
download and parse through multiple files when using signing/release
tools.

Change-Id: I6f845fc055e4ef2ed4adf9628cca505e99b2a9fa