Fix kubectl-cost crashing on systems without glibc by disabling CGO for all builds

[michaelmdresser]

How does this PR impact users? (This is the kind of thing that goes in release notes!)

• Fix kubectl-cost crashing on systems without glibc by disabling CGO for all builds

Links to Issues or ZD tickets this PR addresses or fixes

• Closes Error: GLIBC not found #147

How was this PR tested?

Before

→ make build      
cd cmd/kubectl-cost && govvv build

→ ldd cmd/kubectl-cost/kubectl-cost 
	linux-vdso.so.1 (0x00007fff9ada9000)
	libresolv.so.2 => /usr/lib/libresolv.so.2 (0x00007fc0aa7a5000)
	libc.so.6 => /usr/lib/libc.so.6 (0x00007fc0aa5be000)
	/lib64/ld-linux-x86-64.so.2 => /usr/lib64/ld-linux-x86-64.so.2 (0x00007fc0aa7cb000)

After

→ make build
cd cmd/kubectl-cost && CGO_ENABLED=0 govvv build

→ ldd cmd/kubectl-cost/kubectl-cost
	not a dynamic executable