ci: set number of make jobs globally and decrease to 5 jobs

ci: set number of make jobs globally and decrease to 5 jobs

Summary:
travis docs explicitly state that the expectation for builds is to have
2 cpus, meaning that 10 jobs is wayyyy too many and was actually causing
some build failures due to strain on the virtual hw

this sets the number of jobs using a global variable to avoid having to set
it separately for each build

https://docs.travis-ci.com/user/reference/overview/#Virtualization-environments

Reviewers: devilhorns, ManMower

Reviewed By: ManMower

Subscribers: ManMower, cedric, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D6558