Fixed nameclash with mysql-connector-python. The fix makes

Fixed nameclash with mysql-connector-python. The fix makes module directory (collectors_path) higher priority over
site-packages.

If mysql-connector-python any MySQL-python is installed, the diamond silently tries to load mysql-connector-python's "mysql", which will make the module not get registered. 

Without the fix: 
[2013-09-10 17:06:50,804] [MainThread] Loading Collectors from: /usr/share/diamond/collectors/mysql
[2013-09-10 17:06:50,810] [MainThread] Loaded Module: mysql55
[2013-09-10 17:06:50,810] [MainThread] Loaded Collector: mysql55.MySQLPerfCollector
[2013-09-10 17:06:50,810] [MainThread] Loaded Module: mysql
[2013-09-10 17:06:50,810] [MainThread] Loading Collectors from: /usr/share/diamond/collectors/mysql/test
[2013-09-10 17:06:50,811] [MainThread] Loading Collectors from: /usr/share/diamond/collectors/loadavg
[2013-09-10 17:06:50,814] [MainThread] Loaded Module: loadavg


With the fix: 
[2013-09-10 17:07:11,296] [MainThread] Loading Collectors from: /usr/share/diamond/collectors/mysql
[2013-09-10 17:07:11,308] [MainThread] Loaded Module: mysql55
[2013-09-10 17:07:11,309] [MainThread] Loaded Collector: mysql55.MySQLPerfCollector
[2013-09-10 17:07:11,309] [MainThread] Loaded Module: mysql
[2013-09-10 17:07:11,309] [MainThread] Loaded Collector: mysql.MySQLCollector
[2013-09-10 17:07:11,310] [MainThread] Loading Collectors from: /usr/share/diamond/collectors/mysql/test
[2013-09-10 17:07:11,310] [MainThread] Loading Collectors from: /usr/share/diamond/collectors/loadavg
[2013-09-10 17:07:11,311] [MainThread] Loaded Module: loadavg