bugfix: fix volume size without unit

[rudyfly]

Ⅰ. Describe what this PR did

fix volume size without unit, such as size=1024 will be failed.

Ⅱ. Does this pull request fix one issue?

NONO

Ⅲ. Describe how you did it

check the size has unit or not, if it has no unit size, we will add "B" at the end of size.

Ⅳ. Describe how to verify it

# pouch volume create -d local -o size=1048576 -n test
Mountpoint:   /data/pouch/volume/test
Name:         test
Scope:
Status:       map[sifter:Default size:1048576 mount:/data/pouch/volume]
CreatedAt:    2018-4-25 21:28:44
Driver:       local
Labels:       map[]

Ⅴ. Special notes for reviews

Signed-off-by: Rudy Zhang rudyflyzhang@gmail.com

[codecov-io]

Codecov Report

Merging #1215 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #1215      +/-   ##
=========================================
+ Coverage   15.66%   15.7%   +0.04%     
=========================================
  Files         171     171              
  Lines       10393   10398       +5     
=========================================
+ Hits         1628    1633       +5     
  Misses       8645    8645              
  Partials      120     120

Impacted Files	Coverage Δ
pkg/bytefmt/bytefmt.go	89.83% <100%> (+0.94%)	⬆️

[yyb196]

LGTM

[Letty5411]

tests LGTM