Make project go version more explicit

Make project go version more explicit

- define GO_VERSION variable in build.sh that determines which go version
  is used to build the binaries
- align go version to 1.14 that is defined in all go.mod files [0]
- bump snapshot version to 0.10.3-SNAPSHOT

[0] the mod files all declared 1.13, but 1.14 was effectively used for the build

Issue-ID: MULTICLOUD-1520
Change-Id: I790db4352206ffe6a213472ec8e195b08ae423f4
Signed-off-by: Fiete Ostkamp <fiete.ostkamp@telekom.de>