fixes CC-595: save serviced script log to: /var/log/serviced/script-2014-12-18-083236.log

https://jira.zenoss.com/browse/CC-595

DEMO - installing deb should create new dir /var/log/serviced with rwxrwxrwxt perms:
```
# plu@plu-9: sudo dpkg -i 'serviced_1.0.0~trusty_amd64.deb'
Selecting previously unselected package serviced.
(Reading database ... 209085 files and directories currently installed.)
Preparing to unpack serviced_1.0.0~trusty_amd64.deb ...
Unpacking serviced (1.0.0~trusty) ...
Setting up serviced (1.0.0~trusty) ...
Installing new version of config file /etc/default/serviced ...
Processing triggers for ureadahead (0.100.0-16) ...

# plu@plu-9: ls -al /var/log/serviced
total 8
drwxrwxrwt  2 root root   4096 Dec 18 09:58 .
drwxrwxr-x 15 root syslog 4096 Dec 18 09:58 ..
```

DEMO - serviced script captures stdout/stderr to timestamped log file in /var/log/serviced:
```
# plu@plu-9: serviced -v=1 script run -n expected-to-fail.txt
Logging to logfile: /var/log/serviced/script-2014-12-18-101237-plu.log
I1218 10:12:37.582887 29300 script.go:108] syscall.exec unix script with command: [/usr/bin/script --append --return --flush -c serviced -v=1 script run -n expected-to-fail.txt /var/log/serviced/script-2014-12-18-101237-plu.log]
Script started, file is /var/log/serviced/script-2014-12-18-101237-plu.log
I1218 10:12:37.601707 29312 script.go:115] runScript filename:expected-to-fail.txt &{ServiceID: DockerRegistry: NoOp:false TenantLookup:<nil> Snapshot:<nil> Commit:<nil> Restore:<nil> SvcIDFromPath:<nil> SvcStart:<nil> SvcStop:<nil> SvcRestart:<nil> SvcWait:<nil>}
open expected-to-fail.txt: no such file or directory
Script done, file is /var/log/serviced/script-2014-12-18-101237-plu.log

# plu@plu-9: cat /var/log/serviced/script-2014-12-18-101237-plu.log
Script started on Thu 18 Dec 2014 10:12:37 AM CST
I1218 10:12:37.601707 29312 script.go:115] runScript filename:expected-to-fail.txt &{ServiceID: DockerRegistry: NoOp:false TenantLookup:<nil> Snapshot:<nil> Commit:<nil> Restore:<nil> SvcIDFromPath:<nil> SvcStart:<nil> SvcStop:<nil> SvcRestart:<nil> SvcWait:<nil>}
open expected-to-fail.txt: no such file or directory

Script done on Thu 18 Dec 2014 10:12:37 AM CST

# plu@plu-9: id
uid=1000(plu) gid=1000(plu) groups=1000(plu),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),108(lpadmin),124(sambashare),999(docker)
```