crda: Throw verbose error message if M2Crypto is missing
crda: Throw verbose error message if M2Crypto is missing

Instead of throwing a cryptic Python backtrace, throw a better error message, if
the M2Crypto module is not installed.

Signed-off-by: Michael Buesch <77666125932addc6fc525b281b518fd8fd2203d8@bu3sch.de>

CyanogenMod/android_external_crda,idor/crda,ThirdProject/android_external_crda,idor/crda,CyanogenMod/android_external_crda,ThirdProject/android_external_crda