Updating javadoc for DPM apis

Added @throws tag in the javadoc for many APIs which might throw a
SecurityException in cases when such information might be useful for the
caller. E.g. when the caller has to be a device owner or must request
certain policies before making the API call.

Bug: b/27532288
Change-Id: I18e1a49a5e86a0322c035996ed7e9c3217da78c8
2 files changed