Save volume ratio as integer value to the config file

Save volume ratio as integer value to the config file

- Issue:
According to the app locale, sometimes the framework can fail to get
proper background volume ratio value from the configuration file.

- Solution:
This patch fixes the logic for saving background volume ratio value.
According to the spec. of snprintf() and atof(), these functions are
affected by the app locale. Thus, the app can represent the floating
point value with different way by the locale. And this can cause the
failure of getting proper value.
To avoid this situation, this patch converts the volume ratio as integer
value. Through this change, the locale will not affect the
representation for the volume ratio.

Change-Id: Ieb5c80098b91d56801b98183e8c524db6cf1b0bc
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>