JCBC-140: Throw ConnectionException during config bootstrap on invalid URI.

This changeset throws a ConnectionException instead of a ParseException
to make it more clear what is happening during bootstrap. The exception
is thrown when the /pools URI can not be read properly, this mainly
occurs when /pools is omitted in the host list and therefore index.html
gets used.

Change-Id: I2bdc072d95727610758e4068a6793bf0c5bcd85b
Reviewed-on: http://review.couchbase.org/23648
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Deepti Dawar <deepti.dawar@globallogic.com>