appended signatures: Parse ASN1 node

appended signatures: Parse ASN1 node

This code allows us to parse ASN1 node and allocating memory to store it.
It will work for anything where the size libtasn1 returns is right:
 - Integers
 - Octet strings
 - DER encoding of other structures

It will _not_ work for things where libtasn1 size requires adjustment:
 - Strings that require an extra NULL byte at the end
 - Bit strings because libtasn1 returns the length in bits, not bytes.

If the function returns a non-NULL value, the caller must free it.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Sudhakar Kuppusamy <sudhakar@linux.ibm.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Avnish Chouhan <avnish@linux.ibm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>