Fix coding convention about member variables and static functions

Fix coding convention about member variables and static functions

- Issue:
Using two underscores(__) as name of variables or functions is
reserved by C and CPP compilers, so it may occur name colision.

- Solution:
Previously, most of the code followed old tizen coding convention.
However, in case of name, the convention conflicts with C and CPP
standard, because two underscore is already reserved as an identifier by
C and CPP standard. Thus, using two underscores may cause some problems.
To resolve this collision, this patch fixes the name of member variables
and static functions to match C and CPP standard. Through this patch,
CPP files in the project do not use two underscore as name of variables
and functions anymore.

Change-Id: I0ab5030b018d0d28c9cf2927ddbdf8711ecb788b
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>