Assign return values to individual variables

Assign return values to individual variables

- Issue:
One variable is used as return value for many functions and they have
different purpose.

- Solution:
vconf_str is used for return values of many vconf_get_str(). It is very
common usesage, but it also cause misuse because developer can not
directly know the meaning of value from the name of variable. So this
patch makes variables for return value of each vconf_get_str() calling
and names them more meaningful name.

Change-Id: I69eb1314795e569d0dc10444aa299380e6412237
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>