cyrus-sasl: several fixes

1. Fix hardcoded libdir
2. configure cyrus-sasl based on PACKAGECONFIG
3. create user by inherit useradd
4. add -fPIC to CFLAG to fix the below building failure:
        ld: ../sasldb/.libs/libsasldb.a(db_berkeley.o): relocation R_X86_64_32S against
        `.rodata' can not be used when making a shared object; recompile with -fPIC
        ../sasldb/.libs/libsasldb.a(db_berkeley.o): could not read symbols: Bad value
   The cause is that libsasldb.a is built twice since {.c.o: and .c.lo} co-exist, one
   with -fPIC, other without -fPIC. if no -fPIC library follows behind, this error
   will appear. so we enable -fPIC no matter whatever objects are built.
5. The version of db in oe-core is 5.0

Signed-off-by: Roy.Li <rongqing.li@windriver.com>
Signed-off-by: Joe MacDonald <joe.macdonald@windriver.com>