Right merge not preserve order
Base by [SO question](https://stackoverflow.com/q/57092373/2901002):

Merge with right join not preserve order of columns:

    columns = ['A', 'B', 'C']
    data_1 = [[2, 5, 3, 5], [8, 2, 4, 1], [6, 5, 9, 1]]
    data_1 = np.array(data_1).T
    df_1 = pd.DataFrame(data=data_1, columns=columns)
    print (df_1)
       A  B  C
    0  2  8  6
    1  5  2  5
    2  3  4  9
    3  5  1  1
    
    columns = ['A', 'B', 'C']
    data_2 = [[2, 5, 3, 5], [7, 1, 3, 0], [np.nan, np.nan, np.nan, np.nan]]
    data_2 = np.array(data_2).T
    df_2 = pd.DataFrame(data=data_2, columns=columns)
    print (df_2)
         A    B   C
    0  2.0  7.0 NaN
    1  5.0  1.0 NaN
    2  3.0  3.0 NaN
    3  5.0  0.0 NaN
    
    #right join NOT preserve order
    df1 = df_1.merge(df_2[['A', 'B']], on=['A', 'B'], how='right')
    print (df1)
       A  B    C
    0  5  1  1.0
    1  2  7  NaN
    2  3  3  NaN
    3  5  0  NaN
    
Correct order for right join:
        
        A   B   C
    0   2   7   NaN
    1   5   1   1
    2   3   3   NaN
    3   5   0   NaN
    
    #left join wpreserve order correct
    df2 = df_1.merge(df_2[['A', 'B']], on=['A', 'B'], how='left')
    print (df2)
       A  B  C
    0  2  8  6
    1  5  2  5
    2  3  4  9
    3  5  1  1


----

    print (pd.show_versions())
    
    INSTALLED VERSIONS
    ------------------
    commit: None
    python: 3.7.3.final.0
    python-bits: 64
    OS: Windows
    OS-release: 7
    machine: AMD64
    processor: Intel64 Family 6 Model 60 Stepping 3, GenuineIntel
    byteorder: little
    LC_ALL: None
    LANG: en
    LOCALE: None.None
    
    pandas: 0.24.2
    pytest: 4.3.1
    pip: 19.0.3
    setuptools: 40.8.0
    Cython: 0.29.6
    numpy: 1.16.2
    scipy: 1.2.1
    pyarrow: None
    xarray: None
    IPython: 7.4.0
    sphinx: 1.8.5
    patsy: 0.5.1
    dateutil: 2.8.0
    pytz: 2018.9
    blosc: None
    bottleneck: 1.2.1
    tables: 3.5.1
    numexpr: 2.6.9
    feather: None
    matplotlib: 3.0.3
    openpyxl: 2.6.1
    xlrd: 1.2.0
    xlwt: 1.3.0
    xlsxwriter: 1.1.5
    lxml.etree: 4.3.2
    bs4: 4.7.1
    html5lib: 1.0.1
    sqlalchemy: 1.3.1
    pymysql: None
    psycopg2: None
    jinja2: 2.10
    s3fs: None
    fastparquet: None
    pandas_gbq: None
    pandas_datareader: None
    gcsfs: None
    None