• Improve some errors logs

Description

While Redis is down sometimes we are crashing:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x13f6f01]

goroutine 12648760 [running]:
bosun.org/cmd/bosun/sched.(*Schedule).CheckNotifications(0xc0110fc600, 0x0, 0x0, 0x0)
        /builddir/build/BUILD/bosun-0.8.0/GO/src/bosun.org/cmd/bosun/sched/notify.go:68 +0x1e1
bosun.org/cmd/bosun/sched.(*Schedule).dispatchNotifications(0xc0110fc600)
        /builddir/build/BUILD/bosun-0.8.0/GO/src/bosun.org/cmd/bosun/sched/notify.go:30 +0x1ee
created by bosun.org/cmd/bosun/sched.(*Schedule).Run
        /builddir/build/BUILD/bosun-0.8.0/GO/src/bosun.org/cmd/bosun/sched/alertRunner.go:18 +0xa4

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How has this been tested?

• Interaction test with Redis crashing emulation

Checklist:

• This contribution follows the project's code of conduct
• This contribution follows the project's contributing guidelines
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules