log: use one write system call per message

log: use one write system call per message

Two separate safe_write calls would result in having two write syscalls
like so:

    25098 write(2, "2016-10-04 11:33:46.357326 7fb025968f00 10 client.4143 did not get mds through better means, so chos"..., 114) = 114
    25098 write(2, "\n", 1)                 = 1
    25098 write(2, "2016-10-04 11:33:46.357333 7fb025968f00 20 client.4143 mds is 0", 63) = 63
    25098 write(2, "\n", 1)                 = 1
    25098 write(2, "2016-10-04 11:33:46.357336 7fb025968f00 10 client.4143 send_request rebuilding request 1 for mds.0", 98) = 98
    25098 write(2, "\n", 1)                 = 1
    25098 write(2, "2016-10-04 11:33:46.357341 7fb025968f00 20 client.4143 encode_cap_releases enter (req: 0x7fb02e7502c"..., 110) = 110
    25098 write(2, "\n", 1)                 = 1

Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>