A bug in rank() function in package LinearAlgebra

``` julia
julia> using LinearAlgebra
julia> df=ones(200,2);
julia> rank(df)
1
julia> df=ones(500,2);
julia> rank(df)
2
julia> versioninfo()
Julia Version 1.1.0
Commit 80516ca202 (2019-01-21 21:24 UTC)
Platform Info:
OS: Linux (x86_64-pc-linux-gnu)
CPU: Intel(R) Core(TM) i7-4790 CPU @ 3.60GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-6.0.1 (ORCJIT, haswell)
Environment:
JULIAPATH = /home/sunsh/software/julia-1.1.0/bin
```

Start by reproducing the rank() examples from the issue with Julia 1.1.0 and inspect the LinearAlgebra rank() entry point. Compare the results for ones(200, 2) and ones(500, 2); done means the inconsistent rank results are understood and corrected, with regression coverage for the reported cases.

Written by the indexing model from the issue text.