adb: configure /system file permission with fs_config

adbd changes the permissions of files uploaded by copying
owner's permission to group and other. This causes kernel
load failure if any changes are made to kernel modules
followed by ``adb push'' or ``adb sync'' because file mode
644 would become 666.

The change uses fs_config to get the target mode of files.

In addition, the SELinux file label is set incorrectly
on synced files. Set the label properly.

Change-Id: I354db848f39adfbf189d7e8d3b028e8d763c772f
Signed-off-by: Liang Cheng <licheng@nvidia.com>
Bug: 12264775