Description of problem:
Log to the journal natively instead of /var/log/dnf.log and /var/log/dnf.rpm.log.

Version-Release number of selected component (if applicable):
dnf-0.4.10-1.fc20.noarch

Additional info:
dnf could use some extra fields to describe better (for machines, not humans) what's going on, e.g. PACKAGE (could be kernel, glibc, firefox etc), ACTION (could be update, erase, install etc).

Some log entries in JSON format from yum-3.4.3-128.fc20.noarch:
{
        "__CURSOR" : "s=6be9d5d77524476e8c316f4852d3bfdb;i=22d07;b=3065e3978f8a444e849ac39ae54bc0a6;m=46077a7087;t=4ef14a73176ad;x=9f3d01efc2168f",
        "__REALTIME_TIMESTAMP" : "1388771890263725",
        "__MONOTONIC_TIMESTAMP" : "300773175431",
        "_BOOT_ID" : "3065e3978f8a444e849ac39ae54bc0a6",
        "PRIORITY" : "6",
        "_UID" : "0",
        "_GID" : "0",
        "_MACHINE_ID" : "865b8ff295c29b42a3eef3ecebbeea5a",
        "_HOSTNAME" : "hermes.home.cristian.ciupitu.ro",
        "_CAP_EFFECTIVE" : "1fffffffff",
        "_TRANSPORT" : "syslog",
        "SYSLOG_FACILITY" : "1",
        "_AUDIT_SESSION" : "1",
        "_AUDIT_LOGINUID" : "5000",
        "_SYSTEMD_CGROUP" : "/user.slice/user-5000.slice/session-1.scope",
        "_SYSTEMD_SESSION" : "1",
        "_SYSTEMD_OWNER_UID" : "5000",
        "_SYSTEMD_UNIT" : "session-1.scope",
        "_SYSTEMD_SLICE" : "user-5000.slice",
        "SYSLOG_IDENTIFIER" : "yum",
        "_COMM" : "yum",
        "_EXE" : "/usr/bin/python2.7",
        "_SELINUX_CONTEXT" : "unconfined_u:system_r:rpm_t:s0-s0:c0.c1023",
        "SYSLOG_PID" : "3444",
        "MESSAGE" : "Updated: dnf-0.4.10-1.fc20.noarch",
        "_PID" : "3444",
        "_CMDLINE" : "/usr/bin/python /bin/yum --enablerepo=*-testing update dnf",
        "_SOURCE_REALTIME_TIMESTAMP" : "1388771890262566"
}
{
        "__CURSOR" : "s=6be9d5d77524476e8c316f4852d3bfdb;i=22d57;b=3065e3978f8a444e849ac39ae54bc0a6;m=4622a75187;t=4ef14c25e57ae;x=2768b29ad362964a",
        "__REALTIME_TIMESTAMP" : "1388772346189742",
        "__MONOTONIC_TIMESTAMP" : "301229101447",
        "_BOOT_ID" : "3065e3978f8a444e849ac39ae54bc0a6",
        "PRIORITY" : "6",
        "_UID" : "0",
        "_GID" : "0",
        "_MACHINE_ID" : "865b8ff295c29b42a3eef3ecebbeea5a",
        "_HOSTNAME" : "hermes.home.cristian.ciupitu.ro",
        "_CAP_EFFECTIVE" : "1fffffffff",
        "_TRANSPORT" : "syslog",
        "SYSLOG_FACILITY" : "1",
        "_AUDIT_SESSION" : "1",
        "_AUDIT_LOGINUID" : "5000",
        "_SYSTEMD_CGROUP" : "/user.slice/user-5000.slice/session-1.scope",
        "_SYSTEMD_SESSION" : "1",
        "_SYSTEMD_OWNER_UID" : "5000",
        "_SYSTEMD_UNIT" : "session-1.scope",
        "_SYSTEMD_SLICE" : "user-5000.slice",
        "SYSLOG_IDENTIFIER" : "yum",
        "_COMM" : "yum",
        "_EXE" : "/usr/bin/python2.7",
        "_SELINUX_CONTEXT" : "unconfined_u:system_r:rpm_t:s0-s0:c0.c1023",
        "SYSLOG_PID" : "4031",
        "_PID" : "4031",
        "MESSAGE" : "Installed: yum-plugin-priorities-1.1.31-19.fc20.noarch",
        "_CMDLINE" : "/usr/bin/python /bin/yum install yum-plugin-priorities",
        "_SOURCE_REALTIME_TIMESTAMP" : "1388772346188103"
}