Handle empty list items

[jjo93sa]

Add select() filter to the creation of grub_cmdline_linux_new removes empty list elements, which might exist in kernal_cmdline as a result of defaults, For example, consider the list:

kernel_cmdline:
  - processor.max_cstate=1
  - intel_idle.max_cstate=0
  - default_hugepagesz={{ controllers_perf_tuning_default_hugepagesz }}
  -  hugepagesz={{ controllers_perf_tuning_hugepagesz }}
  - hugepages={{ controllers_perf_tuning_hugepages }}
  - transparent_hugepage={{ controllers_perf_tuning_transparent_hugepage }}
  - "{{ vendor_iommu_setting }}"
  - iommu=pt
  - "{{ pcie_aspm_setting | default(None) }}"
  - "{{ rcu_nocbs_setting | default(None) }}"

This results in:

grub_cmdline_linux_new:
  - console=tty0
  - console=ttyS0,115200
  - no_timer_check
  - nofb
  - nomodeset
  - gfxpayload=text
  - net.ifnames=1
  - processor.max_cstate=1
  - intel_idle.max_cstate=0
  - default_hugepagesz=1G
  - hugepagesz=1G
  - hugepages=512
  - transparent_hugepage=always
  - intel_iommu=on
  - iommu=pt
  - ''
  - ''

And, when those empty list elements are appended to the string, two additional white spaces are added to the end of the string. This can break idempotency of the role.

grub_cmdline_linux_new: 'console=tty0 console=ttyS0,115200 no_timer_check nofb nomodeset gfxpayload=text net.ifnames=1 processor.max_cstate=1 intel_idle.max_cstate=0 default_hugepagesz=1G hugepagesz=1G hugepages=512 transparent_hugepage=always intel_iommu=on iommu=pt  ' # notice the spaces between "t" and the closing quote

[markgoddard]

Thanks