standalone_test: unset log level on root logger

Other modules may have messed with the root logger already, so if we
don't reset the root logger log level, messages go through the logger
even after we add the console and file handlers later.

This problem wasn't visible before because an autotest module was
unconditionally setting the root logger log level to DEBUG, but a recent
patch I sent to autotest removes that unconditional logging setup code.

This patch also renames configure_logging() to reset_logging(), as it
doesn't configure any handler, but just remove the existing logging
configuration).

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
virttest.virt_vm: Update regex pattern of check guest kernel panic

When kernel raise oops with BUG() macro, the oops message is
like following, so the pattern needs some update to match this
format of oops.

"""
------------[ cut here ]------------
kernel BUG at /root/module/test.c:9!
invalid opcode: 0000 [#1] SMP
Modules linked in: test(OF+) ipt_MASQUERADE tbios_ns  virtio_blk [last unloaded: test]
CPU 1
Pid: 2451, comm: insmod Tainted: GF          O 3.7.5-201.fc18.x86_64 #1 Bochs Bochs
RIP: 0010:[<ffffffffa00db009>]  [<ffffffffa00db009>] test_init+0x9/0x10 [test]
RSP: 0018:ffff88001c847f18  EFLAGS: 00010246
RAX: ffff88001c847fd8 RBX: ffffffffa00dd000 RCX: 0000000000000034
RDX: 00000000000006e0 RSI: 00000000000000fb RDI: ffffffffa00db000
RBP: ffff88001c847f18 R08: ffff88001fc14740 R09: 0000000000000080
R10: ffff88001e03ff98 R11: 0000000000000000 R12: ffffffffa00db000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS:  00007f24fd8f8740(0000) GS:ffff88001fd00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00007fd595188000 CR3: 000000001bfd7000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process insmod (pid: 2451, threadinfo ffff88001c846000, task ffff8800196d5c80)
Stack:
 ffff88001c847f48 ffffffff8100216a ffffffffa00dd000 0000000000014ba0
 0000003dcce103e1 0000000000000000 ffff88001c847f78 ffffffff810c2ce0
 0000003dcce103e1 00000000018ff350 0000003dcce103e1 00000000018fe090
Call Trace:
 [<ffffffff8100216a>] do_one_initcall+0x12a/0x180
 [<ffffffff810c2ce0>] sys_init_module+0xc0/0x220
 [<ffffffff8163e199>] system_call_fastpath+0x16/0x1b
Code: <0f> 0b 0f 1f 44 00 00 0f 1f 44 00 00 55 31 c0 48 89 e5 5d c3 0f 1f
RIP  [<ffffffffa00db009>] test_init+0x9/0x10 [test]
 RSP <ffff88001c847f18>
---[ end trace 2f1dfbcce63b1426 ]---
"""

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>