Fix a common mistake about errno(3) usage

Fix a common mistake about errno(3) usage

[Issue#]   N/A
[Problem]  errno may have been changed by other system call.
[Cause]    errno should be preserved.
[Solution] Save errno to a local variable

[Remarks] ERRNO(3)

A common mistake is to do

    if (somecall() == -1) {
        printf("somecall() failed\n");
        if (errno == ...) { ... }
    }

where  errno  no  longer  needs  to have the value it had upon return from somecall()
(i.e., it may have been changed by the printf(3)).
If the value of errno should be preserved across a library call, it must be saved:

if (somecall() == -1) {
    int errsv = errno;
    printf("somecall() failed\n");
    if (errsv == ...) { ... }
}

Change-Id: Ib407b8a7b1cd13d37c3f182c4c28f059bb1749ea