scripts: add possibility to not override default connection timeout

Allow '-1' to be specified as CONNECTION_TIMEOUT to disable the use
of the connection timeout for wget.

Signed-off-by: Cody P Schafer <dev@codyps.com>
Message-Id: <cb33f8c2cbaf802d4f04.1399687632@localhost>
Patchwork-Id: 347582

 # m68k specific configuration file

 ## select ARCH_SUPPORTS_32

 ## select ARCH_DEFAULT_32

 ## select ARCH_DEFAULT_BE

 ## select ARCH_SUPPORTS_WITH_CPU

 ##

 ## help The m68k architecture